If I understood your question correctly, there's no way that thalassemia trait can cause 2ry polycythemia in Fe deficiency. Please remember that their is a defect in the globin chain.
Polycythemia with Fe deficiency presents with: high hematocrit (Hct),low mean corpuscular volume (MCV), high hemoglobin, and a high RBC count.
Before there is a decrease of Hemoglobin in iron deficiency, the step before that is a decrease in iron stores; with reduced serum ferritin and marrow iron stores.
Dr yasmin taha
MD clinical pathology hematology and immunology
Consultant hematology and immunology